For the control or adjustment of the grinding roller spacings in a flour milling plant at present essentially four solution proposals exist. The first and oldest solution proposal consists of regulating and controling the grinding rollers by the operator (miller). In order to be able to "manually" perform such a control operation, it is absolutely necessary to completely control the complete production sequence. The result of the control is largely dependent on the skill and experience of the operator, who is generally the miller. If it is necessary to use less skilled personnel, e.g. during special periods (holidays, night work, etc.), this can lead to less satisfactory results being obtained by the mill, e.g. through a smaller quantity of light flour being produced or the like.
A second control proposal is described in the journal "Die Muhle und Mischfuttertechnik" of Sept. 3, 1965. The essense of this known proposal is the use of trial screening. During production an absolute classification into the individual particle fractions is not sought, because this would lead to an excessively long screening time and would also cause modifications to the product quality. If e.g. the product being ground is subject for an excessively long period to a screening process, then the screenings also contain fine husks, which would normally float on the top of the material in gyratory sifter operation and would then be discharged as waste. In the case of the theoretical treatment of milling or grinding, it is not possible to take account of such fine points, because they are also dependent on the manner of operation of the preceding and following process machines, i.e. not only the milling per se. In the sense of a complete and absolute regulation of the milling work, it is therefore logical to subject the material being milled to a separate, precise laboratory screening and carry out corrections if variations occur. Although the proposed trial or test screening is more precise, it is not always possible to obtain a representative picture in practice, because the work of the gyratory sifter is, as stated, a combination of screening and sifting and requires a specific product layer over the screen mesh.
Another control possibility is described in EP-B1-13 023 and is based on the fact that any future development in the field of food processing should no longer fundamentally be directed at displacing humans. In fact many processes can be performed faster and less expensively by direct human intervention. Thus, the ever increasing knowledge of the almost complete interlinking of all processes increasingly requires human monitoring and control in cereal processing plants. It has been found that it is not worthwhile to have equipment perform all the processes which the human can monitor, check and manually control.
Another known theoretical proposal for controling a mill (DE-C-2 413 956) aims at replacing the operator, particularly the miller by computers and regulating means. It is based on incorporating the knowledge and experience of the miller in the computer programs and render any routine action on the part of the human superfluous by using independent regulating means. According to this proposal all the grinding rollers are set to a given grinding result on the basis of a previously worked out scheme, namely the ratio of material which does to that which does not pass through the screen. However, a corresponding practical realization of this proposal has not hitherto taken place.
On the basis of the latter prior art, the problem of the present invention is to so improve a control method of the aforementioned type that whilst greatly reducing expenditure an almost fully automatic operation is made possible, accompanied by operational reliability and without any rocking risk, as well as proposing a milling plant for performing such a method.
In the case of a method of the aforementioned type, this is achieved according to the invention in that the test signal is derived only from the screenings or rejected waste material of the screening system and is only supplied to the computer from certain selected key passages.
The measures according to the invention increase the ease of operation and the overall control is left in the hands of the miller. This makes it possible to avoid "oscillation" of the complete milling procedure, i.e. there are no rocking processes, which for many manipulations constitute a considerable hazard. The necessary number of interventions are kept to a minimum and are performed by an experienced person. One or more corrections for the preset control values can, according to the invention, only be performed within the framework of an overall survey, because centrally all the actual values, including those of the key passages, are available at all times and an intervention can be performed in a planned manner, without there being any need for any given fixed correction program. If a fault does occur, the major fault can be removed first, followed by the consequent faults. In the milling field it is considered that the milling as such must not be controlled by complicated regulating means. In connection with the milling of grain, it has not hitherto proved possible to bring all the effective parameters into theoretically or mathematically determinable forms. It is known that the same objective can often be achieved in different ways. It is often a question of the special experience of the miller and his knowledge of plant-specific data. Furthermore milling or grinding is the result of using corresponding groups of machines. The actual milling or grinding work is predetermined to a not insignificant extent by the machine designer, the nature of the operation and the maintenance to the machines, as well as the machines specifically used, the treatment diagram and the special features of the plant, so that there are limits to the way in which the miller can qualitatively influence the milling work.
A further complex which has not been paid much attention up to now is the question of quantitative milling work. It has been found that the quantitative milling work is a very important factor, particularly with a view to automation efforts. With respect to the qualitative evaluation, the human being with his sense and intuition is superior as compared automation tendencies through the use of machines, particularly with regards to milling intermediate products, but this does not apply with regards to the quantitative evaluation. The operator, such as the miller cannot be everywhere in the mill at the same time. The product flow therein is partly fixed by established preset values and largely the individual products automatically find their way into the product flow, the human acting in a regulating manner at certain important crossing points. However, by means of the information obtained at selected key passages according to the invention, an up to date picture of the complete process sequence is always available, even after interventions by the miller. The knowledge of the conditions at the key passages provides, together with the total output, conclusions as to what is happening on most of the machines requiring less extensive supervision. Thus, the invention constitutes a lucky chance with respect to the use of sensible automation, whilst still allowing intervention by the miller. The inventive method for the first time makes use of the surprising finding that when using test results from only a few selected key passages and their processing in a following computer, it is possible to achieve a largely automated control of the milling roller spacings in a cereal milling plant, without it being necessary to evaluate a vast number of other test results through corresponding complicated computing programs, because deliberately a residual intervention possibility on the part of the miller is planned in.
The invention permits various very advantageous development possibilities. At the B passage it is sufficient to e.g. simultaneously determine the mill input capacity, whilst at the C passages it is advantageous if the input capacity of each automatically monitored rolling frame is simultaneously determined. It is completely sufficient when there are very few product changes, if the test signal is determined during the milling process on the basis of the rejected waste material quantity of the first coarse flow (B.sub.1 passage), preferably at short time intervals. In the case of frequent or very frequent changes to the raw material or end product quality, it is preferably to derive the test signal at passages B.sub.2 and possibly further passages (B.sub.3 etc.) on the basis of the screen reject or coarse flow quantity. In a particularly preferred manner, apart from the test signal derived from the screen reject or coarse flow quantity in the B passages, a further test signal is derived from the screenings or flour quantity at passages C.sub.1, once again preferably at short intervals during the measuring or testing process and is supplied to the computer. As a function of the size and ease requirements at the milling or grinding passages, corresponding test values can be derived at the C.sub.2 passages and possibly further passages selected in planned manner. In a particularly preferred manner, the test signal is derived from the quantity of the rejected material or screenings for the following passage combinations: EQU B.sub.1 +C.sub.1 EQU B.sub.1 +B.sub.2 +C.sub.1 EQU B.sub.1 +B.sub.2 +B.sub.3 +C.sub.1 +C.sub.2 EQU B.sub.1 +B.sub.4 +C.sub.1 +C.sub.4.
The latter combination for deriving the measured value is based on the idea that with passages B.sub.1 and C.sub.1 a regulating process is ensured, whereas passages B.sub.4 and C.sub.4 serve for control or checking purposes only. Only particularly preferred combinations for deriving the test signal at particularly important test points are given, but they can be chosen and used by the Expert as a function of the particular milling plant.
According to a further preferred development of the inventive method, the computer stores for each cereal mixture or for each milling function a preset value -- desired value diagram containing all the values for the automatic control of the grinding roller spacings, particularly the preset values corresponding to the grinding gap, together with the minimum and maximum values for the coarse material or flour valid for the subsequently determined gyratory sifter and within which no desired values for the rolling frames are to be changed. This avoids an undesired, overfrequent correction of the roller settings. Thus, at least in theory, a single grinding gap correction at the first coarse material roller frame in a large milling plant leads to change in the conditions at the following twenty to thirty rolling frames and gyratory sifters. Thus, preferably a correction program is associated with the computer, which automatically carries out correction instructions by modifying the operating desired values in the order from the largest to the smallest correction. Thus, if a considerable variation is established at selection passage C.sub.1, then this is corrected first, followed e.g. by the necessary following correction at passage B.sub.1, etc.
It is also very advantageous if the computer contains a basic program, which includes non-automatically detected parameters, (such as e.g. the grinding pressure, power absorption, effective grinding gap width, etc.), particularly also those of non-automatically controlled machines (i.e. non-automatic adjustable or regulatable rolling frames and derived values with respect to the screening work) and can be polled at any time in such a way that, based on earlier values, it is possible to carry out checks and corresponding interventions. This solution makes particularly obvious the usefulness of the automatic means for all the necessary checks and manipulations. It also leads to the advantage that for every shift in a mill, the miller can make use of earlier values. This also makes it possible to ensure a relatively constant operational control of the milling plant, even in the case of personnel changes. It is sufficient in most cases if automatic presetting of the grinding gap only takes place on some of the rolling mills and only on part of said automatically preset rolling mills is a measurement made of the material which does and/or does not pass through the screen, from which the test signal is derived. Thus, preferably only in the case of part of all the rolling mills is there an automatic presetting of the grinding gap and only in part of the automatically presettable rolling mills is the material which does/does not pass through the screen measured can the test signal derive therefrom, so that preferably in less than half of all the rolling mills is the grinding gap automatically preset and in two to six following gyratory sifters is there a measurement of the material which does or does not pass through the screen and the derivation of a test signal therefrom.
According to a particularly advantageous further development of the inventive method, the test signal is derived from instantaneous values of the force fractions, as well as the inflow momentum of the product flow, together with the weight thereof in a weighing vessel, the screenings and/or screen rejection material during continuous operation by determining said instantaneous values over a short period of time, a control quantity is derived therefrom, used for automatic monitoring is optionally used for controlling the rolling frames. It is remarkable that clearly all earlier tests based on continuously operating momentum measuring systems failed. In such continuous weighing systems conclusions are drawn regarding the product quantity on the basis of the momentum of a falling product flow, which leads to relatively good results under ideal conditions. However, if disturbing quantities occur, e.g. the flour starts to stick to the baffle plates, the measured value is rapidly falsified to such an extent that it becomes unusable. Account can easily be taken of this problem in the inventive method, in that by a simple subtraction of two shortly following measurements in a weighing container, the momentum part and therefore any problem source such as atmospheric humidity, product sticking, etc. can be obviated. However, this momentum measurement requires a continuous inflow of material into the weighing container, so that the measurement can be termed continuous. If the aim is an improvement to the uniformity of the product flow in the milling plant, then the value of an intermediate weighing, which is substantially continuous, is frequently performed and only takes a short time. The use of a measured value (as in conventional methods), which in itself represents a disturbance quantity and whose avoidance was the object of the measurement and regulation used, is pointless, as has been demonstrated in the past. According to an advantageous further development of the inventive method for the purpose of determining the control quantity, the weight increase in the weighing vessel is determined without interrupting the product flow per unit of time, the determined value is compared with the complete mill capacity and as a parameter for the sifting unit is then supplied to the computer. Weighting is then preferably carried out in the weighing vessel according to a predetermined cycle, preferably every ten to thirty minutes and it lasts less than 10 seconds, preferably less than 5 seconds.
The invention also aims at a cereal milling plant with a sequence of rolling frames and gyratory sifters, in which the grinding rollers have setting means with controllable drive means and the gyratory sifters are followed by a weighing system for automatically determining the sifting work, whilst a central computer with data store is provided for setting and monitoring the grinding roller setting according to preset desired values and in particular for performing the inventive method. According to the invention this cereal milling plant is characterized in that a momentum weight measuring system for continuously determining the sifting work is associated with the gyratory sifter or sifters. The measured values obtained can, without any disturbing quantity being obtained from the product characteristics, be determined with the precision of balance measured values and nevertheless the advantage of a continuous measuring process, much as with a conveyor-type weigher is obtained. The essential difference compared with the conveyor-type weigher is the very simple construction and the correspondingly low manufacturing costs, such as can otherwise only be obtained with the much more fault-prone momentum measuring means. The inventive milling plant has a number of advantages encountered in conveyor-type weighers and continuous flowmeters, but without having their disadvantages.
Preferably the grinding rollers can be controlled or regulated by means of the computer on the basis of an actual - desired value comparison for the purpose of setting or regulating corresponding operating parameters (grinding roller speed and/or grinding gap) adjustable by means of the grinding rollers. Once again, the setting means or their drive means are preferably remotely controllable by a central computer and there is mechanical or electric coupling between the drive means and the setting means. This solution is preferably used at grinding passages, i.e. on smooth rollers. In the case of coarse material passages or with grooved rollers, the setting means or the drive means for the same is preferably remotely controlled by the computer and is provided for preventing harmful controls with a pressure or distance or force absorption limiting device.